Soil addition improves multifunctionality of degraded grasslands through increasing fungal richness and network complexity

Soil addition is now widely used in the restoration of degraded ecosystems, but how soil addition influences multiple ecological functions of degraded grasslands, and whether these effects depend on the amount and type of soil inoculum, are still not clear. We performed two parallel experiments to examine how two different donor soil types and two amounts of donor soil addition affect the restoration of degraded grassland. In a field experiment at a degraded grassland site where the top layer of the soil was removed (5 cm), we assessed the effect of addition of soil collected from two different ecosystems (upland meadow and meadow steppe) and addition of different amounts of soil (0 cm, 1 cm and 3 cm) on ecosystem multifunctionality. In a microcosm experiment, we examined the effects of soil biotic and abiotic factors on ecosystem functions by inoculating sterilized and non-sterilized soil. Soil addition promoted the restoration of degraded grassland, particularly when higher amounts of soil were added. Both biotic and abiotic factors increased ecosystem multifunctionality. Biotic factors, especially fungal richness and network complexity, had the strongest positive effects on ecosystem multifunctionality. Our study reveals the importance of fungal communities in soil for improving ecosystem multifunctionality in restoration of degraded grassland. Future studies should explore the effects of joint addition of arbuscular mycorrhizal fungi and saprophytic fungi on the ecosystem functions of degraded grasslands.